Use of isometric and isokinetic strength measurements has helped many athletic trainers, exercise physiologists, physical therapists, and others to reliably measure voluntary production of force, power, torque and work. Although there have been ample studies concentrated on the knee, quadriceps, shoulder, and back, the reliability of the ankle has not been well studied. The purpose of this research was to conduct reproducible strength measurements of ankle plantar flexion over a 10 week period. Seven healthy subjects, ranging in physical activity from moderate to active, were studied. The subjects were tested on three different occasions week 1 (W1), week 5 (W5), and week 10 (W10). The neutral position (0_) was set at a 90_ angle between the foot and the tibia. Maximal isometric strength was tested with the ankle at the defined 0_ neutral position and at 10_ plantar flexion. Maximal voluntary contractions (MVCs) were performed for 5 seconds. Isokinetic contractions were per formed between the neutral position and the maximal plantar flexion position that the subjects experienced as being comfortable. Isokinetic strength was measured at angular velocities of 30, 60, 120 and 180 degrees/sec. Maximal isokinetic endurance was tested by monitoring fatigue and total work done over 50 repeated isokinetic plantar flexions at 60_/sec. y. For all strength tests the coefficient of variation over the three measurements ranged between 1 and 8%. The highest degree of reproducibility was found in the isometric and isokinetic strength measurements at low speeds. Interclass correlation coefficients for isometric and isokinetic peak torques at rates of 30o/sec and 60o/sec ranged from 0.89 to 0.93 (p<0.0001). The isokinetic endurance test, however, showed a higher degree of variance. This study suggests that measurement of isometric and, to a lesser extent, isokinetic strength can potentially be used as a reliable, diagnostic tool to monitor patients' rehabilitation and recovery of strength following ankle joint trauma, disuse and consequent skeletal muscle atrophy in surrounding plantar flexors.